05 February 2014

20 January 2014

Press Releases

It’s complicated - new insights into the evolutionary history of bears

Frankfurt am Main, Germany, June 11th, 2014. According to researchers of the LOEWE Biodiversity and Climate Research Centre (BiK-F), Goethe University Frankfurt and the U.S. Wildlife Service, several bear species that today only occur in America or in Asia have hybridized during their evolutionary history. The Beringia land bridge, which connected the habitats of these species in former times, might have enabled their encounter. The large-scale study is based on the comparison and analysis of genetic material from all extant bear species. The results have been published recently in the journal Molecular Biology and Evolution.

Whether in documentaries or in the zoo - everyone has seen and knows about brown bears, polar bears and giant pandas. However, there are several other bear species in Asia and South America that are less well-known, such as the sloth bear, the Asian black bear or the spectacled bear. There are eight bear species that still exist worldwide. Despite many years of research, the exact relationships between them remain unresolved.

Who with whom? Polar bear and brown bear have hybridized Previous analyses of genetic material of polar bears and brown bears have proven already that the two species have hybridized during their long evolutionary history. This behavior can still be observed today and the ongoing climate change drives the bears even closer. It is therefore likely that there have been similar exchanges of genetic material between other species of the bear family.

... as well as brown bears and black bears To shed light on this, a team of the German Biodiversity and Climate Research Centre (BiK-F) and the Goethe University Frankfurt in cooperation with colleagues from the US have now analyzed certain genome parts of all bear species alive today. "We were able to show that several bear species have hybridized during their evolutionary history. The exchange can still be traced in the genetic makeup of today's bears," says the lead author of the study, Verena Kutschera (BiK-F). This mix-up makes it difficult to classify some gene fragments as belonging to a particular species.

Beringia land bridge serving as an intercontinental meeting point Surprisingly, several bear species which nowadays live on different continents have also taken part in the mating and thus gene exchange. This may have been possible because the significantly lower sea level during past ice ages resulted in a land bridge between Asia and North America, the Beringia land bridge. Thus the ancestors of today’s bear species, e.g. of the Asian black bear and the American black bear, had the opportunity to meet and to mate.

Darwin’s species tree is insufficient to map complicated relationships All eight bear species that occur today are well adapted to their present habitat and differ physically very much. A prime example for this are polar bears and black bears. Nevertheless, the speciation has not finished yet at some individual genes, which additionally complicates the research of the evolution of bears.

With new molecular methods more genes might be discovered in the genomes of mammal species that could originate from other species. Apparently separate genetic lineages turn out to have merged – sometimes repeatedly – during the evolutionary history and exchanged genetic material with each other. "The traditional pedigree introduced by Darwin is not always suitable to map evolutionary history in full detail. So-called phylogenetic networks a more useful to depict the genetic mix-up that we have found ", comments evolutionary biologist Prof. Dr. Axel Janke, BiK-F, leader of the research team. The study demonstrates that evolution often is not a linear process; thanks to modern molecular methods its complex processes can finally be revealed.